Technical Field
The present invention relates to a sheet feed device including a detachable sheet feed tray.
Background Arts
Generally, an image forming apparatus for printing images or texts on print sheets (papers), a copy machine for copying images or texts on copier sheets (papers), a sheet processing machine for operating various processes to sheets (papers) and so on are provided with a sheet feed device for feeding sheets (papers).
For example, a Patent Document 1 (Japanese Patent Application Publication No. 2010-173750: this application was filed by the preset applicant) discloses a sheet feed feeder. The sheet feed device disclosed in the Patent Document 1 (whose drawings are not shown in this application) is disposed at a lower portion of a main body of an image forming apparatus, and includes plural detachable sheet feed trays. The sheet feed device supplies sheets to an image forming unit of the image forming apparatus.
In the above-mentioned sheet feed device, three detachable sheet feed trays are disposed vertically at a front lower portion of a main body of the sheet feed device so as to cope with different paper sizes. Each of the sheet feed trays can be drawn out from the main body to the front side. With respect to each of the sheet feed trays, an uppermost sheet is selectively fed forward among plural sheets stacked on each of the sheet feed trays.
A following explanation will be made by taking one of the sheet feed trays in the above-mentioned sheet feed device as an example. A detachable sheet feed tray detachably installed in the main body of the sheet feed device has a height that enables to accommodate 500 sheets of plain papers (normal papers) that is one package unit. A bottom plate is provided at a lower portion of the sheet feed tray via a lifter plate (movable plate) so as to be moved up and down by the lifter plate, and plural papers all having an identical size are stacked on the bottom plate.
When the sheet feed tray is installed in the main body, the lifter plate is lifted up by its drive source, and thereby a leading-side portion (in a sheet feed direction) of the uppermost sheet of the stacked papers is moved upward to au upper limit position so as to face to an after-described sheet feeder. The upper limit position is preliminarily set at an almost constant height level according to a height of the sheet feed tray regardless of the number of papers stacked on the bottom plate.
A sheet feed mechanism is provided above the sheet feed tray in the main body, and a base of the sheet feed mechanism extends longitudinally along an insertion direction of the sheet feed tray into the main body. The sheet feed mechanism also includes a scraper roller and a pickup roller (sheet feed roller). The scraper roller and the pickup roller serve as the above-mentioned sheet feeder, and are disposed at the center of the base along a longitudinal direction of the base. The scraper roller and the pickup roller are aligned from upstream to downstream along the sheet feed direction in this order.
The scraper roller on the upstream side is supported swingably via swing arms that are pivotally attached to a rotational shaft of the pickup roller on the downstream side. The scraper roller is driven by a rotational force of the pickup roller via a transfer gear set
The scraper roller swingably supported by the swing arms will be evacuated to an upper position so as not to contact with the sheet feed tray when the sheet feed tray is draw out from the main body of the sheet feed device and when the sheet feed tray is inserted into the main body of the sheet feed device. However, the installation of the sheet feed tray in the main body is completed, (leading-side portions of stacked papers are moved upward and) the scraper roller is moved downward, and thereby the scraper roller is contacted with the uppermost paper of the stacked papers.
The pickup roller on the downstream side is connected with its rotational drive source, and faces to a handling unit disposed beneath the pickup roller. Even when the rotating scraper roller draws plural papers from the sheet feed tray, the pickup roller and the handling unit feed (handle) only the uppermost paper to the image forming unit disposed on a downstream side therefrom.
A sheet detector is also provided on the base near the scraper roller and the pickup roller, the sheet detector includes a swingably-movable sheet detection wheel. The sheet detector detects whether or not a paper is remained on the bottom plate of the sheet feed tray. In addition, an upper limit detector is further provided on the base near the scraper roller and the pickup roller, and the upper limit detector also includes a swingably-movable upper limit detection wheel. The upper limit detector detects whether or not the leading-side portion of the uppermost paper is positioned at the upper limit position.
The sheet detection wheel and the upper limit detection wheel are attached to the base so as not to contact with the sheet feed tray when the sheet feed tray is draw out from the main body of the sheet feed device and when the sheet feed tray is inserted into the main body of the sheet feed device. Further, a position adjuster is also provided on the base, and the position adjuster adjusts a position of the upper limit detector. The position adjuster is provided with an operative portion disposed on a front side of the main body of the sheet feed device (the image forming apparatus).
According to the sheet feed device disclosed in the Patent Document 1, the position of the upper limit detector can be adjusted by the position adjuster from the front side of the main body without drawing out the sheet feed tray from the main body, so that an operator can adjust the position of the upper limit detector accurately while watching a positional relation between the upper limit detector and the sheet feed tray. In addition, the operator can also adjust the position of the upper limit detector easily.